Usage:
$finder->depth('> 1') // the Finder will start matching at level 1.
$finder->depth('< 3') // the Finder will descend at most 3 levels of directories below the starting point.
See also:
DepthRangeFilterIterator
See also:
NumberComparator
publicdepth ( string | integer$level ) : Finder | Symfony\Component\Finder\SplFileInfo[]